This invention relates to epoxy resin coating formulations. In one aspect, the invention relates to high-solids epoxy-based coating formulations which are curable by multifunctional amine curing agents.
High-performance coatings for protection of metal surfaces of ships, aircraft, bridges and other structures exposed to corrosive environments must be resistant to the corrosive effects of water and solvents. Excellent coating properties can be obtained from the use of solvent-borne, two-package epoxy coatings cured with amine curing agents.
To achieve sufficiently low viscosity to apply high-performance coating formulations, low molecular weight solid epoxy resins may be diluted with solvents. Prohibitions on the use of large quantities of certain solvents for this purpose, however, make it necessary to develop alternate approaches to reducing the viscosity of epoxy-based coating formulations.
A conventional technique for viscosity reduction is the addition of a diluent such as dibutyl phthalate, butyl glycidyl ether, cresyl glycidyl ether or aliphatic alpha alcohol glycidyl ether. Such diluents, however, can adversely affect coating properties and in some instances contribute to the volatile organic compound (VOC) content of the coating. Alternatively, a lower molecular weight liquid epoxy resin and blends of such resins with solid epoxy resins may be employed to reduce the volatile content of coating formulations. A related approach includes the use of low viscosity, nonvolatile curing agents to reduce coating formulation viscosities.
While all of these approaches reduce the viscosity of the coating formulation, they have a tendency to increase the dry time of the resulting coatings. High-performance coatings for metal surfaces of large structures such as bridges must be cured under ambient conditions, as the application of heat over such a large surface is not practical. Ambient-cure dry time is therefore a very important consideration, because a tacky coating picks up dust and is easily marred.
It is therefore an object of the invention to provide a high-solids epoxy-based coating formulation. It is an object of a specific aspect of the invention to provide high-solids epoxy-based formulations curable by a variety of multifunctional amine curing agents. It is a further object to provide a high-solids coating composition which dries rapidly.